1. Field of the Invention
The present invention relates to an optical displacement detecting apparatus, and more particularly to a miniaturized displacement detecting apparatus constructed by fabricating a reflective scale and a sensor head that has a light-emitting device and photosensitive devices mounted thereon.
2. Description of the Related Art
It is well known that there are two types in optical encoders. One is a reflection type that detects a light reflected from scale gratings, and the other is a transmission type that detects a light transmitted through scale gratings. Among those, the reflection type encoder has an advantage in miniaturizing and thinning itself compared to the transmission type because a sensor head, which includes a light source and a photoreceptor, can be constructed only on one side of the scale. The sensor head of the reflective encoder, however, currently has a complicated structure that requires an appropriate frame to fabricate a substrate having photosensitive devices mounted thereon, a light-emitting device such as an LED, and a printed wire board for connecting these devices.
Therefore, the conventional reflection type encoder has a disadvantage in its complicated structure in order to produce a compact and thin encoder that can be integrated in a small X-Y table, for example. It also requires a lot of assembly man-hours and is difficult to achieve automated manufacturing and mass production.
The inventors have previously proposed a technology for realizing a miniaturized sensor head using a resin block (U.S. Pat. No. 5,995,229).
The present invention is directed to further improve the technology of the earlier application and accordingly has an object to provide an optical displacement detecting apparatus capable of further miniaturizing and thinning a sensor head.
The present invention is provide with an optical displacement detecting apparatus, which includes a reflective scale having scale gratings formed thereon with a certain pitch. It also includes a sensor head movably located relative to the reflective scale for emitting a light to the reflective scale and receiving reflected light from the reflective scale to generate a displacement signal. The sensor head comprises a lead frame. It also comprises an LED chip mounted on the lead frame at a and having a light-emitting surface for irradiating the reflective scale. The sensor head further comprises a photosensitive device chip mounted on the lead frame at a location apart from the LED chip and having a photosensitive surface for receiving a reflected light from the reflective scale. The photosensitive surface of the photosensitive device chip and the light-emitting surface of the LED chip are opposite in direction. The sensor head also comprises a transparent resin body molded for sealing the LED chip and the photosensitive device chip mounted on the lead frame therein. It further comprises a reflective film formed on the surface of the transparent resin body for reflecting the light emitted from the LED chip to irradiate the reflected scale.
According to the present invention, the sensor head is constructed by mounting the photosensitive device chip and the LED chip on the lead frame and integrally molding them with a transparent resin. This allows the sensor head to be miniaturized and thinned. In addition, power supplying to the light-emitting and photosensitive devices can be centralized in one position so that wiring spaces are possibly reduced. The photosensitive device chip and the LED chip are mounted on the lead frame so that their photosensitive surface and light-emitting surface are opposite in direction. In addition, the reflective film is formed on the surface, which faces on the LED chip, of the transparent resin body so as to reflect the light from the LED chip to irradiate the reflective scale. This allows the sensor head to gain a high sensitivity.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.